What is the difference between VAR and VIM? Legacy Vimscript Variables vs. Modern Neovim API

At its core, the distinction between "VAR" and "vim" is a distinction between a legacy data storage system and a modern, comprehensive programming interface. A "VAR" refers to a traditional Vimscript variable (like g:my_var), which is a simple key-value store. In contrast, vim is the global Lua object in Neovim that provides a structured, powerful, and complete API for interacting with every aspect of the editor.

In short, think of a Vimscript variable as a simple Post-it note you stick somewhere in the editor. The vim object, however, is the entire control panel, giving you access to the editor's engine, settings, and functions through a clean and modern interface.

Understanding "VAR": The Vimscript Variable System

The term "VAR" isn't a formal keyword but represents the traditional method of storing state in Vim using Vimscript variables. This system is defined by its use of special prefixes to denote scope.

The Role of Scoped Prefixes

Vimscript variables are always preceded by a prefix that defines their lifetime and visibility. Understanding these is key to understanding the old system.

• g: (Global): Accessible everywhere, across all tabs, windows, and buffers. This is the most common for user configuration and plugin settings.
• b: (Buffer): Tied to a specific buffer (a file loaded into memory). Useful for storing buffer-local information, like compiler flags for a specific file.
• w: (Window): Tied to a specific window (a viewport onto a buffer).
• t: (Tab): Tied to a specific tab page.
• v: (Vim-internal): Reserved for variables defined by Vim itself, like v:count.

The Core Concept: Direct State Mutation

Working with these variables involves directly setting or getting a value in a specific scope. In Vimscript, you use let g:my_var = 'value'. In Neovim's Lua, you would use vim.g.my_var = 'value'. In both cases, you are directly manipulating a global key-value dictionary.

Understanding "vim": The Neovim Lua API

When developers refer to vim, they mean the primary entry point for all interactions with Neovim from a Lua environment (init.lua or Lua plugins). It is a global Lua table that acts as a structured and well-documented namespace.

A Programmatic and Structured Interface

Unlike the scattered nature of Vimscript variables, the vim object organizes access to the editor's internals into logical sub-modules. This makes code easier to write, read, and debug.

Key API Submodules

The vim object contains many modules, but a few are fundamental for replacing traditional Vimscript patterns:

• vim.g and vim.b: These are Lua tables that act as a bridge to access global (g:) and buffer-local (b:) Vimscript variables. Setting vim.g.my_var is the same as setting g:my_var.
• vim.o: A direct, structured way to get and set editor options (e.g., vim.o.tabstop = 4), which is far superior to the old set tabstop=4 command.
• vim.fn: A bridge to call any built-in Vimscript function (e.g., vim.fn.expand('%') to get the current file path).
• vim.api: The core of Neovim. This provides a stable, fast, and feature-rich set of functions for manipulating buffers, windows, and the editor state in a programmatic way.

Understanding the Trade-offs: Legacy vs. Modern

Choosing between these two approaches depends entirely on your goal, specifically whether you prioritize compatibility with older Vim versions or the power and clarity of the modern Neovim ecosystem.

The Case for Vimscript Variables

The primary reason to use the g:var style is portability. If you are writing a plugin or a configuration snippet that must run on both standard Vim and Neovim, you must use Vimscript. It is the common denominator.

The Case for the vim Lua API

For any work targeting only Neovim, the vim API is vastly superior. It offers structure and discoverability (your language server can provide autocompletion for vim.api.*), significantly better performance via LuaJIT, and improved safety through a well-defined API rather than direct state mutation.

The vim.g Bridge: The Best of Both Worlds

The vim.g table is the critical link. When writing a Neovim plugin in Lua, you use vim.g to define configuration variables. This allows your users to configure your plugin using either traditional Vimscript (let g:my_plugin_setting = 1) in their init.vim or Lua (vim.g.my_plugin_setting = 1) in their init.lua.

Making the Right Choice for Your Goal

Your decision should be guided by your specific context—whether you're writing a personal configuration, a public plugin, or a cross-compatible script.

• If your primary focus is a personal Neovim configuration (init.lua): Default to the vim Lua API for everything (vim.o, vim.keymap.set, vim.api). It is faster, cleaner, and more maintainable.
• If your primary focus is writing a modern Neovim plugin: Build your internal logic using the vim.api and other Lua modules. Expose user-facing settings via vim.g to provide a stable configuration interface.
• If your primary focus is compatibility with classic Vim: You have no choice but to use the traditional Vimscript variable system (g:, b:, etc.) and Vimscript functions.

By understanding this distinction, you can write more effective, maintainable, and performant editor configurations and plugins.

Summary Table:

Feature	Vimscript Variables (VAR)	Neovim Lua API (vim)
Purpose	Legacy state storage	Modern, structured API for editor control
Syntax	Scoped prefixes (g:, b:, etc.)	Organized modules (vim.api, vim.o, etc.)
Performance	Slower, interpreted Vimscript	Faster, compiled via LuaJIT
Portability	Works in Vim & Neovim	Neovim-only
Use Case	Cross-editor compatibility	Modern Neovim configs & plugins

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